Question

How does the different mechanism of pH maintenance at the cellular and blood level?

Answer 1

There is a normal pH value in each body compartment (i.e. extracellular fluid, plasma, intracellular fluid etc). Intracellular pH is difficult to measure and may vary in different types of cells and in different parts of cells.

Maintaining blood pH between 7.37 and 7.43 creates an optimal environment for cellular enzyme activity and membrane integrity. The body has several mechanisms by which it maintains blood pH in that range, despite dietary and endogenous production of acids and bases. It is estimated that the average child generates 1 to 3 mEq/kg of net acid each day.

The body has three main mechanisms to compensate for acid disturbances :-

The first line of defense consists of the bicarbonate and nonbicarbonate (e.g., hemoglobin, tissue proteins, organophosphate complexes, bone apatite) buffering systems in the plasma and cells.

The second line of defense is the respiratory system. H+ is combined with HCO3− to form carbonic acid (H2CO3), which dissociates to water (H2O) and CO2. CO2 freely diffuses across alveolar barriers and is excreted by the lung.

The third line of defense is the renal system. The kidney maintains acid-base homeostasis by the reabsorption of HCO3− from the glomerular filtrate and the secretion of H+ into the urine.